1. Field of the Invention
Diaryliodonium salts are used as efficient photoinitiators for cationic polymerization. The instant invention relates generally to the synthesis of diaryliodonium salts possessing aliphatic ester groups of differing lengths and, specifically, to novel diaryliodonium salts in which long chain ester groups are attached to the aryl groups. More precisely, diaryliodonium salts of the instant invention possess aryl and aliphatic ester groups bonded to iodine which together comprise an aggregate of more than 20 carbon atoms.
2. Discussion of Relevant Art
A search of the patent literature, as well as the professional journals, reveals that diaryliodonium salts having the structure Ar--I.sup.+ --Ar MX.sub.n.sup.-, where Ar are aryl groups and MX.sub.n.sup.- represents the metal halide anion, serve as efficient photoinitiators for cationic polymerization. In U.S. Pat. No. 4,090,936, issued to Barton for PHOTOHARDENABLE COMPOSITIONS, aforementioned diaryliodonium salts are disclosed wherein the aryl groups are defined as consisting of aromatic groups or arylalkyl groups containing from 6 up to, but not exceeding, 20 carbon atoms. Quite matter of factly, such salts as would contain more carbon atoms are specifically excluded. In a patent recently issued to the instant inventor and incorporated herein by reference: NON-TOXIC ARYL ONIUM SALTS, UV CURABLE COATING COMPOSITIONS AND FOOD PACKAGING USE (U.S. Pat. No. 4,882,201), the invention of non-toxic photoinitiators comprising diaryliodonium salts which possess alkoxy groups of differing lengths is taught. However, no mention is made of similar diaryliodonium salts containing other functional groups having long carbon chains. Most notably, diaryliodonium salts with ester (aliphatic) groups attached to the aryl moieties, together exceeding 20 carbon atoms, are not described therein, nor in the patent or chemical literature.
The instant inventor believed that the organic solubility of diaryliodonium salts could be enhanced if the total number of carbon atoms within the groups bonded to iodine exceeded 20. Quite unexpectedly, he discovered that it is possible to prepare, in good to excellent yield, diaryliodonium salts in which long chain ester groups are attached to the aryl groups, thus providing an aggregate (aromatic-aliphatic) number of carbon atoms in the desired quantities. Incorporation of the long chain ester functions onto the aryl groups does indeed confer enchanced solubility to these salts compared to their lower molecular weight counterparts, a characteristic hereinafter demonstrated.